The invention relates to a method and apparatus for transmitting encoded media data.
Conventionally, in a best-effort transmission line environment such as the Internet, a large volume of encoded packet data (media data) such as streaming information or video telephony is transmitted continuously.
In the best-effort transmission line environment as described above, congestion occurs due to an increase in communication traffic in the network. Quality of media data being transmitted deteriorates noticeably due to this congestion. Techniques for preventing such deterioration in quality of media data include techniques as described below.
One technique, for example, is to use a redundant code such as a Forward Error Correction (FEC) code. Another technique is to use retransmissions such as in an Automatic Repeat Request (ARQ) protocol.
In a FEC system, parity information of the media data is generated and sent from a transmission side, whereby, even in the case where a packet loss occurs on a reception side, it becomes possible to perform restoration of the data of the lost packet.
In an ARQ system, when a packet loss is detected on the reception side, the reception side requests the transmission side to retransmit the lost packet, and the transmission side retransmits the lost packet, whereby it becomes possible to prevent deterioration in quality of the media data.
Further, in the best-effort transmission line environment, conventionally, the deterioration in the quality of the media data due to the packet loss is prevented by the following techniques: a technique that switches between the FEC system, which is effective for a stationary packet loss, and the ARQ system, which is effective for a burst packet loss; and a technique that uses a combination of the FEC system and the ARQ system (e.g., see Patent documents 1 and 2).
Note that, as other related art to the retransmitted invention, for example, there are techniques disclosed in Patent documents 3 to 5 described below.
[Patent Document 1]
Japanese Patent Application Laid-Open Publication No. 7-67175
[Patent Document 2]
Japanese Patent Application Laid-Open Publication No. 2002-330118
[Patent Document 3]
Japanese Patent Application Laid-Open Publication No. 9-214474
[Patent Document 4]
Japanese Patent Application Laid-Open Publication No. 9-298526
[Patent Document 5]
Japanese Patent Application Laid-Open Publication No. 2000-228676